Search

The thickness of the CdS:O window layer plays an important role in CdTe-based thin-film solar cell performance. Normally with thinner CdS:O layer, the cells’ short wavelength response can be enhanced to achieve higher short-circuit current density (Jsc), while the open-circuit voltage (Voc) and fill factor (FF) would degrade. Previous research finds that reducing the CdS:O layer thickness to less than 40 nm would decrease the cells’ efficiency (Eff.). In this work, 18% efficiency CdTe thin-film solar cell with only 30 nm CdS:O window layer is demonstrated. A post annealing process is developed to fabricate high efficiency cells with ultrathin CdS:O layers. Our results indicate that the high defect density in CdTe absorber, low built-in potential (Vbi) and high back contact barrier (Φb) are partially responsible for the reduced Voc and FF of cells with ultrathin CdS:O layers. The post annealing process can increase the carrier concentration (NCV) and Vbi, and decrease the Φb, in which way improves Voc and FF for higher cell efficiency.

Optical detection of pressure has the advantage of direct and dynamic indication of the pressure distribution with a high spatial resolution. In this study, microcrystal (µ-crystal) light-emitting ...

We present broadband MMI couplers, developed for a novel integration platform on InP with active/passive integration capabilities for the 1300nm wavelength range. Low loss (

In this work, etched singlemode-multimode-singlemode (E-SMS) optical fiber structures are evaluated through the implementation of anti-BSA/BSA immunoassay. By tracking the wavelength response, it is found that the E-SMS devices can detect the presence of antiBSA.

Our recently proposed three-step method showed the promising potential to improve the accuracy of relative wavelength response (RWR) characterization in the wavelength-modulation spectroscopy (WMS) over the commonly used summation method. A detailed comparison of the three-step method and the summation method, for the wavelength-scanned WMS gas-sensing, was performed with different laser parameters (modulation indexes and scan indexes) and gas properties (pressures and concentrations). Simulation results show that the accuracy of the predicted gas parameters is strongly limited by the RWR characterization with large modulation index and high gas pressure conditions. Both fitting residuals of RWR and errors of predicted gas parameters from the recently proposed three-step method are nearly 2 orders of magnitude smaller than those from the summation method. In addition, the three-step method is further improved by introducing a coupling term for the 2nd harmonic amplitude. Experiments with CO2 absorption transition at 6976.2026 cm−1 were conducted and validated the simulation analysis. The modified-three-step method presents an improved accuracy in RWR description with at least 5% smaller fitting residual for all conditions compared with the three-step method, although the deviation of the deduced CO2 concentrations between these two methods does not exceed 0.2%.

A novel methodology to directly pre-determine the relative wavelength response (RWR) of a DFB laser, in terms of a combined current linearly scanned wavelength response and current modulated wavelength response (CMWR), in wavelength modulation spectroscopy (WMS) is presented. It is shown that the assessed RWR can be used to mimic the measured response with standard deviation of discriminations that are below 3.4 x 10(-3)cm(-1) under a variety of conditions. It is also shown that its performance supersedes two commonly used assessment models of the CMWR but is slightly worse than that of the third model. however with the benefit of solely using a single fitting parameter (the concentration) instead of more. When the novel method is applied to the assessment of CO2 concentration in a Herriot-type multipass cell by using the technique of calibration-free WMS, the results show that there is virtually no difference compared to that by use of the best of the other methods. It is concluded that the novel method is more robust and simplifies the retrieval process of gas concentration.

We succeeded in hydrogen evolution using InGaN photocatalysts grown on conductive Ga2O3 substrates. These photocatalysts exhibited a conversion efficiency of 0.8% from incident light energy to stored H2 chemical energy. Their quantum efficiency was determined to be more than 1% at 404 nm by incident photon-to-current conversion efficiency (IPCE) measurement. We found that the wavelength response of the InGaN structure can be extended to the visible region. These results indicate that the conductive Ga2O3 substrates are suitable for the photocatalysts.

We describe two component hydrogels with networks composed of self-sorted fibres. The component gelators are based on 1,4-distyrylbenzene (OPV3) and perylene bisimide (PBI) units. Self-sorted gels can be formed by a slow decrease in pH, which leads to sequential assembly. We demonstrate self-sorting by NMR, rheology and small angle X-ray scattering (SAXS). Photoconductive xerogels can be prepared by drying these gels. The wavelength response of the xerogel is different to that of the PBI alone.

Ga 0.51 In 0.49 P solar cells with compositionally-graded (Al z G a1-z )xln 1-x P window-emitter structures, both lattice-matched and pseudomorphically (tensile) strained, were grown via molecular beam epitaxy using a digital alloy based grading approach. Preliminary results suggest that the resulting drift field and elimination of discrete interfaces near the top surface of these devices helps mitigate the impact of surface/interface recombination and sub-optimal window and/or emitter material quality. A significant increase (>10% absolute quantum efficiency) in carrier collection in the UV-blue (λ < 500 nm) was observed, along with a commensurate Jsc increase of ~10% relative versus standard, fixed-composition reference cells.

Solution-processable organic-inorganic hybrid perovskite materials with a wealth of exotic semiconducting properties have appeared as the promising front-runners for next-generation electronic devices. Further, regarding its well photoresponsibility, various perovskite-based photosensing devices are prosperously developed in recent years. However, most exploited devices to date only transiently transduce the optical signals into electrical circuits while under illumination, which necessitates using additional converters to further store the output signals for recording the occurrence of light stimulation. Herein, a nonvolatile perovskite-based floating-gate photomemory with a multilevel memory behavior is demonstrated, for which a floating gate comprising a polymer matrix impregnated with perovskite nanoparticles is employed. Owing to the well photoresponsibility introduced by the embedded nanoparticles, the device is enabled to access multiple wavelength response and the functionalities of recording power/time-dependent illumination under no vertical electrical field. Intriguingly, a nonvolatility of photorecording exceeding three months with a high On/Off current ratio over 104 can be achieved.

Based on the combined effect of mapping more than one resonant wavelength response to microwave frequency, a tunable flat-top bandpass microwave photonic filter is implemented by a single microring resonator and single sideband modulation.

Holograms as spectrum splitting concentrator elements are achieving high relevance in improving overall efficiency of photovoltaic systems. Photopolymer holographic elements have the added advantages of near hundred percent diffraction efficiency, easy recording and handling, lower cost etc. Along with high diffraction efficiency, achieving optimum spectral response is of critical importance here. This paper reports recording of volume holographic elements of 91% optimum diffraction efficiency at 639 nm and the spectral and angular response studies conducted.

The development of highly efficient onium salt-based photoacid generating systems has provided many new opportunities for the design of novel photocuring and imaging systems. This communication focuses on some of the more recent efforts in designing and synthesizing efficient photoacid generating systems with tailored wavelength response. The use of these photoacid generating systems in a number of applications is described.

The magnetic spacing of both longitudinal and perpendicular Ba-ferrite particulate tapes was evaluated in comparison with that of metal particulate tapes. First, the effective spacing, which is the sum of the magnetic spacing and the transition parameter, was determined by fitting the wavelength response to Wallace's equation. Next, the transition parameter was obtained from a magnetic force microscopy image. Finally, the magnetic spacing was calculated as the difference between the effective spacing and the transition parameter. Both the transition parameter and the magnetic spacing of both longitudinal and perpendicular Ba-ferrite particulate tapes were much smaller than those of metal particulate tapes. These results indicate that Ba-ferrite particulate media have a considerable advantage over metal particulate media in high-density recording.

We propose and demonstrate a 1times2 thermooptic digital optical switch with variable optical attenuators that are integrated with the S-bend waveguides connecting the output of the Y-switch with a standard fiber array. With a total heating power of 140 mW applied to the switch, we have achieved less than -42-dB optical crosstalk. The wavelength response of the switch is flat across the entire C-band. The average polarization-dependent loss of the switch is about 0.49 dB

A novel Frequency Selective Surface (FSS) conflguration is proposed for the design of polarization-insensitive metamaterial absorbers operating below 1GHz, where the flrst resonances of small commercial enclosures appear. The novel FSS shows a strong sub- wavelength response, enhanced by the dielectric substrate, which allows the design of compact planar absorbers with excellent angular and polarization stability.

It has been reported that high-density and wide-bandwidth characteristics may be obtained by using a ring head with obliquely oriented metal evaporated magnetic recording tape. We therefore developed new equipment for the preparation of obliquely oriented tapes based on ?-Fe 2 O 3 particles, and examined the morphology, magnetic properties, and wavelength response of the tapes. The experimental results showed that tape with an oblique orientation of 30° has the highest output and widest bandwidth characteristics.

The theory, fabrication, and performance of monolithic 4 x 4 single-mode fused couplers is reported. The field coupling matrix is derived and used to show that a device having equal coupling between the four fibers may be obtained. The fabrication of such a device is described, and measurements show that the device exhibits excellent coupling uniformity and low excess loss. The wavelength response of a device designed for equal coupling at 1.53 microm is shown between 1.2 and 1.6 microm.

In this work we report on the optimization of the p-GaN window layer for InGaN/GaN solar cells. We studied the effect of p-GaN thickness and growth temperature on the electrical performance. By optimizing the window thickness of In x Ga 1−x N solar cells with X In ≈0.04 we maximized short wavelength response and produced solar cells with 82% FF and Voc of 2 V and enhancement of Jsc of 80% over un-optimized devices. We also studied the effect of growth temperature of the window layer, and found that the electrical performance was greatly improved with higher growth temperatures. By increasing the p-GaN growth temperature from 890 °C to 1040 °C, reverse bias leakage was reduced by three orders of magnitude, Voc increased from 0.85 to 1.65 V and peak output power increased by nearly 100% for devices with X In ≈0.08. Surface pit density was also significantly decreased by increasing growth temperature and seems to be an important mechanism for leakage in these devices.

The effect of filter characteristics on the output performance of actively mode-locked fiber ring lasers has been studied experimentally and numerically, with the same 3-dB bandwidth, the filter that has a flatter wavelength response tends to generate narrower soliton-like pulses.

A rapid, non-destructive optical method for detecting the perpendicular orientation at the surface of metal LIPS tape is described. This technique uses reflection anisotropy due to the depolarization coefficient anisotropy of the acicular metal particles. A tape sample with low anisotropy according to this method of evaluation exhibited higher density wavelength response characteristics.

Ring resonators are coupled in parallel in order to obtain a second order type of wavelength response. The phase relationship between the rings determines the details of the spectral response. The rings used in the experiment have radii of 25 /spl mu/m and are fabricated from compound glass having an index of 1.539. Several resonances are observed to have double peaked box-like response.

A four-channel 400 GHz channel spacing InP-based arrayed waveguide grating with a flattened wavelength response by employing a multimode interference coupler at the input waveguide of the filter is prepared. The fabricated devices show a flattened spectral response with a broadened 3-dB bandwidth up to 3.5 nm, interchannel non-uniformity of

A new scheme to obtain wavelength-insensitive optical fibre couplers, based on group velocity equalisation, is presented. It allows flattened wavelength response over the whole C-band.

Pole-zero diagrams are often employed in electronic filter design because of their simple and direct visualization of spectral characteristics. This paper proposes the use of pole-zero diagrams for tailoring the spectral response of ring resonator array filters for photonic applications. We show that there exist close relations between the pole-zero diagram features of the resonator array and its wavelength response characteristics, and demonstrate that the pole-zero diagram approach could be a very useful tool in the design of photonic devices based on resonator filters. In particular, we employ the pole-zero diagram approach for the case of a parallel-coupled ring resonator array for interleaving, and use this method to produce a new low crosstalk design.

A four-channel phased-array wavelength demultiplexer with a flattened wavelength response has been realised for the first time in InP/InGaAsP at 1.54 mu m by employing multimode output waveguides. The device has 2 nm channel spacing and a flat response (within 1 dB) of 17 nm. >

We demonstrate the first In0.53Ga0.47As/InP p‐doped quantum well infrared photodetector (QWIP). This detector has the shortest wavelength response, λp=2.7 μm, ever achieved in a QWIP and operates at normal incidence.

We propose and experimentally demonstrate a novel method which, for the first time to our knowledge, makes it possible to tailor the wavelength response of a waveguide grating coupler. Such grating couplers may be used to improve the efficiency of broad-band quantum-well infrared photodetectors and solar cells.

In this paper, we present a theoretical study on the effect of the angle of a tilted Bragg grating written in a 2 x 2 symmetric fused fiber coupler. Coupling coefficients and wavelength response curves show that the grating angle is critica1 in determining the behavior of the component. For a particular type of coupler, a tilt of 0.4' is sufficient to degrade component performance.

UV-sensitive products which undergo a colour change on exposure to UV radiation are available for use by the general public. We have evaluated SunCheck patches of various sensitivities, and Tanscan UV sensor cards, in terms of their temperature stability, wavelength response and response to sunlight. The products exhibited no perceptible colour change when the temperature was maintained at 45 degrees C for 4 hours; on exposure to monochromatic radiation, the sensitivity peaked at a wavelength of 335 and 355 nm for SunCheck and Tanscan, respectively; the response to sunlight under clear conditions was reasonably consistent, with the coefficient of variation for each type of material ranging between 12.5 and 27%. These products are based on the incorrect concept that there is a 'safe' dose of UV radiation. Thus, they cannot be recommended to the public as a reliable way of reducing the risk of skin cancer.

Metal stripe waveguides in silica, operating in the fundamental long-range mode and at optical free-space wavelengths near 1550nm, are discussed in detail. Straight and curved waveguides having various stripe geometries are modeled. Au, Ag, and Al are compared as metals for the stripe. The wavelength response of waveguides is computed. The impact of index asymmetry is determined and discussed. The results generated and collected herein should be useful to the design of low-loss metal stripe waveguides for integrated plasmonic applications in silica and cladding materials of comparable index.

A new method for the fabrication of a singlemode fibre wavelength independent Y-junction is described; through asymmetrically tapering a pre-assembled Y-junction precursor, the splice point is drawn into the waist region of the device and low-loss is ensured. The lowest loss and flattest wavelength response for such a device is reported.

Results of calculations are presented which illustrate the effect of the location of an ideal winding on the wavelength response of probe heads from a perpendicular recording medium with a permeable underlayer. Calculated wavelength responses represent the theoretical limits for the response of practical probe heads with practical windings. A numerical estimate of possible improvement of readback response of probe heads is presented.

The readback response of a perpendicular recording system utilizing a medium with a soft magnetic underlayer (SMUL) had been investigated using rigorous two-dimensional theory. The results are as follows. 1) Changes in the medium thickness (with a SMUL) effect radical changes in the wavelength response of the heads. 2) For a thin medium, the effective gap of a ring head becomes twice its geometrical gap. 3) The combination of probe head and medium with SMUL has adequate resolution only if the recording medium thickness is an order of magnitude less than probe thickness. 4) The foregoing combination has a potential advantage over longitudinal recording on conventional thin media with respect to the absolute value of readback output.

A LIPS tape of CrO 2 particles was prepared through the follwing steps: 1) a perpendicular orientation over the entire thickness by the previous "VAST" method (Vertical magnetic orientation-AC demagnetization-Smoothing period -Train), 2) a short radiation heating only in the shallow surface layer and 3) a magnetic reorientation to the longitudinal direction only in the inside layer, still in a low viscosity state. Their magnetic data show that the thickness of the perpendicular surface layer can be controlled to any suitable thin value by the heating condition. Their wavelength response shows both high density and wide band characters.

Barium-ferrite fine-particle-coated perpendicular magnetic recording tapes have been experimentally fabricated. Typical tapes have M s = 120 - 130 emu/cc, H c = 600 - 1500 Oe and perpendicular squareness ratio M_{r\perp}/M_{s} larger than 0.9. Tape recording performances were measured with a perpendicular head as well as With a ring-shaped head. A good short wavelength response, D 50 = 76k FRPI, which has never been attained by longitudinally oriented particulate tapes, was obtained; The relationship between perpendicular squareness ratio and output was also investigated to show the importance of perpendicular orientation for attaining a higher recording density.

Achieving both high resolution and high read/write efficiency has been tried with a rather thick single-pole-head film core having the sensitive (ordinary) trailing edge and the less sensitive leading edge in the neighborhood of which a degradation of the magnetic flux density (Bs) is made. The degradation is made by laminating several sputtered layers of different alloy constitution of Co 1-x Zr x (x = 0.17-0.32). The whole film core consists of this degradation region of 4.2 μm thick and high permeability Co 0.85 Zr 0.03 Nb 0.12 region of 5.0 μm thick. Observed shallowing of the reproduce nulls in the wavelength response with the rather thick core shows a possible compatibility of the resolution and the efficiency.

We report In1−xGaxAsyP1−y/InP photodiode detectors with external quantum efficiencies of 50–70% without antireflection coating. The short‐ and long‐wavelength response limits of these very efficient detectors can be compositionally tuned to lie anywhere in the wavelength range 0.9

Output response of thin film heads was analyzed using wavelength response to determine the optimum pole tip length for both low peak shift and high resolution. From the analytical analysis, thin film heads were designed and fabricated. The experimental results very much agree with the theoretical results. We conclude that by selecting the trailing pole to be thicker than the leading pole we can achieve optimum results for certain linear density requirements. We also observe that heads with thin poles provide better results at both low frequency and high frequency, while heads with thick poles work better at mid range frequency.

The fabrication and performance of a stable single-mode transmissive 8×8 star coupler is described. The device exhibits very low excess loss (0.13 dB), good coupling uniformity (0.73 dB) and low near-end crosstalk (>64 dB). The star coupler is fabricated from eight lengths of single-mode fibre, by forming 3 dB fused coupling regions between appropriate fibre pairs. A Table of insertion loss measurements is presented, together with graphs showing the wavelength response between 1.2 and 1.7 μm.

Barium ferrite media have created a lot of interest for digital and analog applications because of their potential to achieve high recording densities. To fully exploit this potential, it is necessary to develop media with good perpendicular orientation and to employ high saturation narrow gap heads. It is possible, however, to obtain very good recording performance utilizing Ba‐ferrite media which are nonoriented or only partially oriented and ordinary ferrite heads for high‐density digital recording applications. In this study, we investigated the performance of such media in rigid disk form using conventional and narrower gap ferrite heads, and obtained much better short wavelength response than that obtained from high‐coercivity cobalt‐modified iron oxide media. The overwrite modulation of these media, however, is only marginally acceptable. The modulation noise observed is much larger for longitudinally oriented than for perpendicularly oriented media. A simple model is proposed to explain the origin...

The perpendicular recording mode is still a candidate for obtaining higher densities. Best recording results on a double-layer (DL) medium must be expected from using a probe head (PH). This contribution provides an analysis of the write-read performance of one-sided PHs that do not use an auxiliary pole on the back of the medium. Analytical as well as numerical models were used to calculate the effects of saturation and medium thickness on the write fields. Experimental verification of the modeling results was obtained by measuring the wavelength response of many W-shaped PHs on DL media. Combining this with the calculated response, we obtained a semi-empirical relation between the pole nulls, pole thickness and the pole-to-backlayer distance. It reveals a PH behaviour very different from a ring head (RH). The pole thickness calculated from the measured pole-null wavelengths showed a very close agreement with the optically determined value. The calculated head efficiencies are very small, as was confirmed experimentally, and need improvement before the PH has an output comparable with a RH.

The wavelength response of a reproducing head can be estimated quantitatively by the superposition of isolated pulses in perpendicular magnetic recording, because recording demagnetization does not occur. In this paper, the resolution of reproduction of a single-pole head is theoretically investigated for various thicknesses of the main-pole and compared with the experimental results. It is also shown that the 50 % down density D 50 is influenced by the virtual spacing, which depends on the thickness of the Co-Cr layer of a double-layered medium. To realize the high resolution of a single-pole head, the main-pole of 0.15 μm in thickness has been made of a Co-Zr-Nb amorphous film. The 50 % down density D 50 of 135 kFRPI could be reached by combining this head with the double-layered medium having a thinner Co-Cr layer of 0.25 μm.

The twisting of an asymmetric fused tapered single-mode fibre coupler is found to decrease the maximum coupled power, in addition to the usual shift in the wavelength response. This effect can be used to optimise a wavelength-flattened coupler's performance during or after coupler elongation.

Long-wavelength HgCdTe photodiodes operating at 20 K have been developed with quantum efficiencies >40%, bandwidths >500 MHz and a calculated heterodyne NEP = 6 × 10−20 W/Hz for a local oscillator power of 100 μW at 28 μm. A theoretical analysis along with wavelength response, pulse response and noise data are described.